This invention deals with a method and apparatus for recording the surface topology of live skin tissue.
Heretofore, the recording of fingerprints has generally been obtained by coating the fingers with ink and then transferring the ink-formed image onto a piece of paper. This is a very messy and inconvenient method of recording fingerprints, and methods and apparatus for recording fingerprints without the use of ink or other chemicals have not until recently been developed which are sufficiently easy to carry out or use to be feasible for use in police stations and the like.
Many techniques have been developed for recording the surface topology of skin and other tissue. Some of these methods involve taking microscopic pictures of tissue severed from the human body. In such case, recorded images are generally formed on high-resolution silver halide film, requiring a time-consuming developing process which does not make the skin topology involved immediately available to the doctor or researcher. Such processes are not convenient for obtaining the tissue topology of live skin, since it is not feasible to place the particular area of the body involved into the field of a microscope where, to take effective picture, the skin involved must be pressed against a flat surface to obtain perfectly focused images of the entire skin area, while projecting light upon the skin area involved which is necessary to expose the film.
U.S. Pat. No. 3,533,823 to W. H. Newkirk et al discloses a method of making a fingerprint when a finger is pressed upon an imaging material coated on a metal substrate heated to a temperature substantially above room temperature but sufficiently low as not to burn the users fingers. The imaging material is one which has a hysteresis characteristic where the film initially has a very low reflectivity (i.e. black) at room temperature. When elevated above room temperature it progressively becomes more reflective (e.g. approaching a pure red color). The imaging layer has a given degree of reflectivity prior to the application of a finger thereto. When a finger is placed upon the imaging layer, the points thereof contacted by the ridges of the finger cool the same so that these portions of the imaging layer will have a different degree of reflectivity. When the finger is removed from the imaging layer, the portions thereof previously cooled are heated to the same temperature as the rest of the same. However, because of the hysteresis effect of the imaging layer the degree of reflectivity of the previously cooled portions of the imaging layer will be different from those not originally contacted by the ridges of the finger. The pattern of the ridges of the user's finger will, therefore, be present on the imaging layer until the temperature of the imaging layer is lowered to room temperature where all color differentiation therein disappears. A photograph of the original imprint must thus be taken to obtain a permanent record of the fingerprint. The requirement of a camera as part of the process of providing a permanent record of a fingerprint makes the process involved a very unwieldly one. The only advantage of this process over fingerprinting process utilized prior thereto is that it avoids the necessity of using messy fingerprint ink or other chemicals on the finger.
U.S. Pat. No. 3,070,428 to Cohen discloses a process for reproducing negative images of the raised portion of metal surfaces applied to the imaging layers of Thermofax papers or transparencies which must be bulk-heated to substantially elevated temperatures as disclosed in this patent. These temperatures fall in the range of from about 50.degree. to 250.degree. C. The specific examples given in the patent specify 5 or more seconds of heat application to achieve the desired results. The areas of the Thermofax paper engaged by the raised portions of a metal surface are cooled thereby, so that these portions thereof are not affected by the heat, whereas those portions thereof not contacted by the metal surface are heat-imaged to a dark color, black in the example given in the patent.
The process for reproducing negative images of metal surfaces disclosed in this Cohen patent would appear not suitable for making fingerprints. Thus, the necessity of bulk heating the substrate of the papers requires heat application times to raise the temperature of the paper to the high imaging temperatures that would cause at least a risk of serious discomfort and probably would cause a serious risk of burning a user's finger should the process disclosed be used to obtain fingerprints. Also, since heat application time of the order of magnitude of 5 or more seconds is required with the specific recording papers and temperatures disclosed in this patent, there is a risk of smudging the image since the person holding the finger on the paper involved can usually move his finger relative to the paper within that time involved. Also, in such a long period of time, it is possible that heat spreading parallel to the paper can prevent high resolution imaging, even if the user's finger were to remain stationary on the paper for such a long period of time. While imaging times can possibly be reduced by using higher imaging temperatures, this can raise the risk of burning the paper and causing greater discomfort or damage to the user's fingers.
Relatively recently, a fingerprinting system was developed where fingerprints are applied to the back of a check for identifying the person cashing the check. In this system, the user must first impregnate a fingertip with a chemical material after which he presses his chemical coated fingertip upon a chemically treated section of the check (or a pressure sensitive coated paper to be applied thereto) to leave an imprint of his fingerprint thereon. While this fingerprint system avoids the use of messy inks, it, nevertheless, leaves an undesirable chemical odor on the user's finger until it is washed off. Also, the image produced is not always of the most satisfactory clarity, and it is believed that it does not have archival properties which would be necessary, for example, for fingerprinting records which are to be kept for an indefinite period, as in the case of police and security system fingerprint records.
It is, accordingly, an object of the invention to provide a process and apparatus for providing an immediate record of the surface topology of live skin tissue and which do not require conventional photographic equipment or the application of any ink or chemicals to the skin tissue surface involved. A related object of the most preferred form of the invention is to provide a process and apparatus as just described wherein the cost of producing such a record is competitive with said low cost fingerprint systems for use on checks just described.
A further object of the invention is to provide a method and apparatus satisfying one or more of the above-stated objectives which produces a record of live skin tissue surface topologies immediately upon exposure of the recording film to radiant energy, like an Xenon flash lamp or the like, or to externally applied heat, and without using any chemicals or other consumable materials. A still further object of the invention is to provide a method and apparatus as just described which does not raise any serious risk of burning or discomfort to the live skin tissue involved.
Another object of the invention is to provide a method and apparatus satisfying one or more of the above-stated objectives which has such a high degree of resolution that details which are clearly recorded are as small as about 3-5 micron in size.
A further object of the invention is to provide a method and apparatus as described where unskilled personnel can be used to practice the method or operate the apparatus thereof.
Our co-pending U.S. application Ser. No. 937,432, filed Aug. 21, 1978 discloses a method and apparatus which achieves most of the aforesaid objectives where a source of electromagnetic energy is utilized. The recording film used in the method and apparatus disclosed in this application is a dry process recording film, (most advantageously a dispersion-type film as disclosed in this application) which utilizes a substantially opaque layer of an imaging material deposited on a transparent substrate which, upon application thereto of electromagnetic energy of at least a given critical or threshold level, transmits the energy to the imaging material where the energy is absorbed to produce heat, which raises the unheat-sinked portions thereof to a temperature which causes the opaque imaging layer to become relatively transparent. The film involved can be a high contrast film, but it is preferably a continuous tone type of film wherein there is associated with the imaging layer means for varying the degree of transparency achieved in proportion to the temperature of the imaging layer.
The invention disclosed in this application resulted from a discovery that when the ball of a finger was brought against the imaging material coated side of a dispersion recording film and a flash of radiant energy of a Xenon flash lamp lasting for a small fraction of a second, like that commonly used in taking flash photographs (i.e. typically no greater than about 1/1000 second), was applied through the transparent, substrate side of the film during only the period when the finger contacted the film, there was produced an extremely clear transparency fingerprint record where the depressions in the finger surface appeared in the transparent imaged portions of the film and at least the peak portions of the surface appeared in the relatively opaque portions of the film. When the fingerprint was projected in greatly magnified form on a screen or photographic film subsequently developed, microscopically small details, like pores and other minute depressions, become clearly visible. Moreover, when a continuous tone form of film is used, a degree of transparency is produced in the portions of the film confronted by the various portions of the finger in accordance with the intimacy of contact between the various points of the finger surface involved and the recording film, which produces a three-dimensional visual effect. The dispersion types of films disclosed in this application have archival properties and do not require any special storage conditions.
Of great importance is the fact that no risk of discomfort or harm to live skin tissue results from this imaging system since the electromagnetic energy from the flash lamp applied for a very small fraction of a second does not develop a sufficient quantity of heat energy in the imaging layer as to create any discomfort in the user's skin whatsoever.
The dispersion type recording films described above have extremely good archival properties and this fact, together with the fact that a transparency is produced by the process which enables immediate readily projection of the fingerprint image involved onto a projection screen, the heat-sink imaging method and apparatus disclosed in this application are preferable for most applications. For applications where cost considerations are paramount, such as in the application of fingerprints to the rear of checks and the like, and archival properties are not necessary, recording films other than dispersion-type recording films may be more desirable. Thus, another object of the present invention is to provide a method and apparatus for providing an immediate image of live skin tissue without the need for conventional photographic equipment or inks or other chemicals applied to the skin tissue involved and where the recording film utilized need not be the dispersion-type recording films disclosed in the previously identified applications or other films having transparent substrates.
Another object of the invention is to provide a method and apparatus satisfying one or more of the above-stated objectives where the energy for imaging the recording medium may be a source of heat generated externally to the imaging layer and where there is little risk or discomfort or damage to the live skin tissue involved. A related object of the invention is to provide a method and apparatus as just described which are cost competitive with the previously described fingerprint systems for use on checks.